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My quest for deeper perft numbers for 8x8 checkers using has reached depth 28. Below you see the perft(28) breakdown per move, called "divide". As stated before, the numbers were computed on a cluster of machines, optimized with a "hard collision"-free transposition table as well as bulk counting. The move generator does not eliminate duplicate captures.
At this point, the limits of 64-bit unsigned integers have been reached. Although there are obvious ways around these restrictions, this seems a very good time to give this (by now probably insane) project a rest. I have updated this OEIS entry up to depth 26, and may add the higher depths also when I am a bit more comfortable with these most recent results. divide(28)12-16 = 240070833985819919111-16 = 243138619671261187811-15 = 223178752933125981010-15 = 218644635681176173710-14 = 1872427919495823777 9-14 = 2285893686261887442 9-13 = 2969067990365356900 -------------------------- perft(28) = 16377718018836900735

Rein Halbersma recently posted 8x8 checkers perft results for depth 22 with a request for confirmation (because he uses a hash table, he wanted to make sure no "hard collisions" occur). So I verified his results for depth 22 using a distributed, brute force implementation (no hash tables).

The table below shows the perft breakdown per move (called "divide") from the start position for depths 20 to 22.